Rubber printing plate with built-in curvature



April 16, 1963 L. s. KUNETKA 3,085,507

RUBBER PRINTING PLATE WITH BUILT-IN CURVA'I'URE Filed Aug. 24, 1962 2Sheets-Sheet l nvn n a avn nvn nvnvavdmvnvnvwiiivnvn 32,7W/i//////////////////////m A AUAVAVAVA Apnl 16, 1963 L. s. KUNETKA3,035,507

RUBBER PRINTING PLATE WITH BUILT-IN CURVATURE Filed Aug. 24, 1962 2Sheets-Sheet 2 QYg 3,085,507 Patented Apr. 16, 1963 3,085,507 RUBBERPRINTING PLATE WITH BUILT-IN CURVATURE Lawrence S. Kunctka, 900 LakeShore Drive, Chicago, Ill. Filed Aug. 24, 1962, Ser. No. 220,351 16Claims. (Cl. 101-379) This invention relates generally to printingplates and more particularly, relates to an improved rubber printingplate for printing on corrugated fiberboard, said printing plate havinga built-in curvature corresponding substantially to the curvature of theroll or cylinder of the printing press on which the printing plate ismounted. Additionally, said invention provides a novel base or backingmember for the printing surfaces of a printing plate having such apreset curvature.

This is a continuation-in-part of my co-pending application, Serial No.181,522, filed March 22, 1962, now abandoned.

Printing on corrugated board such as is used extensively in themanufacture of cartons and boxes, is done substan tially universally bymeans of direct printing from a rubber die or rubber printing plate. Therubber printer plates customarily are made with the desired type faceeither in relief or reversed or both, and then mounted on the curvedcylinder of a rotary printing machine, for instance. Heretofore, suchrubber printing plates have been formed as flat members. In the mountingof such flat rubber printing plates on the curved cylinders of thepress, undesirable stretching and distortion of the plates occurs whichgives rise to images reproduced by the direct printing on the corrugatedboard which are irregular and disproportionate in size. Further, inconforming the fiat printing plate to the curved cylinder, the rubberplate is bent and stretched to a degree tending to weaken the same,especially in the light of the treatment to which the printing platenormally is subjected during the printing procedure. The stretching ofthe printing plate also re sults in cupping of the type face charactersthereby contributing to distorted imprints. Since the surface of thefiberboard to which the imprints are applied is corrugated in textureand has surface areas unsupported from below between flutes, thecomplexity of the problems encountcred in making a suitable rubberprinting plate is increased. Also, the bent flat plate has a normalbias, against any forced bending thereof so that it tends to return to afiat condition. After being mounted for some time, the edges of theplate curl and the body thereof tends to cup in shape. Because of suchnormal bias in flat plates, heavy staples commonly were used to securethe printing plate on the printing cylinder.

Prior attempts to provide a rubber printing plate for printing oncorrugated fiberboard generally have been unsuccessful in solving theproblems alluded to hereinabove. One attempt has been to form the rubberprinting plate during the molding thereof by using rubber materials ofdifferent durometer characteristics. However, such attempts have beencompletely unsuccessful especially, where the type face of the printingplate is reversed to type in relief. This form of printing surface isknown as solid. In such instances, the relative thickness of the body ofrubber material in which the reverse type faces were formed caused therubber printing plate to curve in a direction opposite to the curvaturedesired in order to permit mounting of the same on a printing roll.Consequently, although the problems have been recognized and there hasbeen a longfelt need for solution of the aforementioned problems, nosuccessful attempts heretofore have been made in this regard.

Accordingly, a major object of the invention is to provide a rubberprinting plate having a built-in curvature so as substantially toconform to the curvature of the printing roll upon which it is to besecured which substantially eliminates all of the problems hereinaboveenumerated.

Another object of the invention is to provide a rubber printing platehaving a built-in curvature which is universally suitable both forrubber printing plates having type faces in relief and reversed, that isto say, having a so-called solid printing surface in which theintelligence is recessed in the printing surface of the printing plate.

Another object of the invention is to provide a curved printing plate ofthe character described, which utilizes different hardnesses of rubberon the top and bottom surfaces of the printing plate, the upper surfaceof the printing plate which includes the type face being made from alayer or lamination of rubber of lower durometer hardness such that, inthe vulcanization process, the lower surface or base of the plate willshrink to provide a curl in the printing plate whereby a built-incurvature is obtained which will conform to the curvature of theprinting cylinder.

Another object of the invention is to provide a curved printing plate ofthe character described which includes a top layer and bottom layer ofdifferent durometer hardness, said bottom layer of rubber beingsubstantially thicker than the upper layer of rubber.

Another object of the invention is to provide a rubber printing plate ofthe character described in which embodiment of the invention, layers ofnon-shrinkable and shrinkable sheet material such as fibrous glass andcanvas, respectively, are sandwiched between the top and bottom layersof rubber.

Another object of the invention is to provide a novel base or flexiblebacking structure for the rubber printing surfaces of a printing plateof the character described, said structure comprising a composite panelof layers of uncured rubber and selected sheet members which are securedtogether so that the composite panel can be shipped and storaged as aseparate article to be used, as needed, by manufacturers of rubberprinting plates. The manufacturers of such rubber printing plates areengaged, usually, for special printing jobs for which the printing plateis to be made. In manufacturing the printing plate, the composite panelembodying the invention is made available in his inventory for finalmolding of the printing plates, to fill his orders,

Other objects of the invention reside in providing a rubber printingplate of the character described which is economical to manufacture,which is easy to secure on a printing cylinder, which substantiallyeliminates distortion of the lettering in the printing face of theprinting plate notwithstanding the built-in curvature thereof, and whichis durable, long-lasting and strong and which eliminates cupping in thesolid areas of the printing surface.

The foregoing and other objects of the invention will become apparentfrom the ensuing disclosure in which a preferred embodiment has beendescribed in detail in the specification and illustrated in theaccompanying drawing. It is contemplated that minor variations in thestructure, proportion, size and arrangement of parts thereof may occurto the skilled artisan without departing from the scope of sacrificingany of the advantages of the invention.

In the drawings:

FIG. 1 is a perspective view of a preferred embodiment of the rubberprinting plate embodying the invention. FIG. 2 is a fragmentarysectional view taken through the printing plate of FIG. 1.

FIG. 3 is a fragmentary enlarged sectional view through a printing platerepresenting an unsuccessful attempt to adapt prior structures to theproduction of curved printing plates.

FIG. 4 is a perspective view showing the printing plate embodying theinvention secured on a printing cylinder.

FIG. 5 is a fragmentary sectional view greatly enlarged taken through acomposite backing structure in accordance with the invention.

FIG. 6 is a greatly enlarged fragmentary type of the sectional viewtaken through a type of the rubber printing plate embodying theinvention, and exaggerated to show details.

Referring now to the drawings, in FIG. 1, the reference character 20identifies generally one embodiment of the rubber printing plate formingthe invention. The printing plate 20 may be seen to have a normallyarcuate configuration providing a curvature therefor which enables theprinting plate easily and readily to conform generally to the curvatureof a printing cylinder 22, such as shown in H6. 4. Thus, upon securingthe printing plate 20 to :a printing cylinder 22, there is not requiredany stretching or radical bending of the rubber printing plate 20 as isthe general occurrence in the case of flat printing plates heretoforeemployed.

Referring to FIG. 2, in the manufacture of the printing plate 20, thereis provided a flexible printing surface by means of a layer 24 of rubberand a base layer or lamination 26 also formed of rubber. The layer orlamination 24 carries the type 28 which may be cut, molded or otherwiseformed by a technique without critical application to the hereininvention. Sandwiched between the top layer 24 and the base or bottomlayer 26 of the printing plate are a pre-shrunk or non-shrinking sheetmember 30 preferably of fibrous glass material, a sheet 32 of suitablefabric such as canvas capable of shrinking and a layer 34 interposedbetween the sheets 30 and 32. As seen in FIG. 2, the pre-shrunk ornonshrinking sheet 30 is located next adjacent the top layer 24 whilethe shrinkable fabric sheet 32 is located next adjacent the base orbottom layer 26.

Either synthetic or natural rubber materials may be employed in makingthe printing plate 20 with cognizance being taken of the type of inkwhich will be used in the printing process. Where the printing inks havean oil base, it will be necessary to use a rubber material which isresistant to such inks. Natural rubber ordinarily will be attacked byprinting ink having an oil base. On the other hand, where the printinginks have an alcohol or water base, the printing plate can be formed ofnatural rubber.

In the manufacture of the printing plates, the top layer 24 is comprisedof a rubber material of from 20 to 50 durometer hardness. The base orbottom layer 26 is comprised of a rubber material having a durometerhardness of from 70 to 90. The layer 34 of rubber between sheets 30 and32 has a durometer hardness of approximately 70. These durometerhardness values are based upon the Shore durometer scale. Thevulcanization of the several layers to form the printing plate iscarried out at approximately 317 Fahrenheit, or without any criticalpressures or temperatures required and known techniques are followed.Because of the different durometer hardnesses and thicknesses of thelayers 24 and 26, during vulcanization, the base layer 26 will shrinkmore than the top layer 24 thereby causing an upward curling or archingof the printing plate. Also, the sheet member 32 will shrink more thanmember 30 further to cause the desired arcuate formation of the plate20. Upon complete curing, the printing plate is removed from thevulcanizing equipment as an arcuate rubber printing plate or one havinga pre-set or built-in curvature therein shown in FIG. 1. Also, duringvulcanization, the rubber enters the interstices of sheets 30 and 32 tobond to them.

Referring to FIG. 6, there is illustrated a phenomenon believed to occurin the finished printing plate 20. As a result of the vulcanizingprocedure in which the sheet member 30, preferably of fibrous glass,does not shrink, said member 30- is forced into layer 24 of rubber whichforms the flexible printing surface. There may occur some compression ofthe rubber of layer 24 adjacent said member 30, especially in theportions of said rubber layer 24 subtending type 28. In any event, thesheet member 30 assumes an upwardly arched or bowed configurationindicated at 39 which has a slightly greater radius of curvature thanthe radius molded into curvature of the printing plate 20. Thus, themember 30 may be likened to a sheet member having a permanent seat inthe same general direction of curvature of the plate 20. It is believedthat the non'shrinkable, non-elastic character of the fibrous glasssheet 30 enables such slight displacement in adjacent portions of rubberlayer 24 so that the sheet 30 can be placed in this condition ofpermanent curved set adjacent the printing surfaces of the slate 20 andassist to maintain the preset curved condition of} the printing surfaceof the plate 20. Note that none of the other layers 26, 32 and 34experience the same phenomenon in the completed plate 20.

Of further consequence in this structure, is the relationship betweenthe dimensions of the several layers one relative to the other andrelative to the overall thickness of the resulting plate 20. The totalthickness of the printing plate 20 from the crown of type 28 to thebottom surface of layer 26, was approximately .255 inch plus or minus.005 inch. The height of the type 28 above the upper surface 36 of layer24, was approximately .150 inch. The layer 24 was approximately .010inch thick, whereas the layer 26 was approximately .045 inch thick. Boththe sheets 30 and 32 were approximately .010 inch thick and the rubberlayer 34 was approximately .030 inch thick. Thus. the bottom layer 26was thicker than the top layer 24 excluding the thickness of the typeface 28. The greater thickness of the bottom layer 26 in addition to thegreater durometer hardness of the rubber of layer 26 was instrumental inobtaining a fixed curvature in the plate 20 after vulcanization wascompleted.

Referring to FIG. 3, there is illustrated a fragmentary portion insection, of a molded rubber printing plate 40 which has an upper layerof soft rubber 42, a bottom layer 44 of harder durometer rubber and areinforcing sheet member 48 of glass fabric bonded therein. The singlelayer 48 of glass fabric has been used by others in making rubberprinting plates, but not the thick /4 inch) plates required for printingon yieldable materials, such as corrugated board. Where a thick plate ismade using the structure of FIG. 3, although in some instances curvaturewas achieved because of the greater degree of shrinkage of the harderrubber layer 44, the results after molding were not reliable. In manycases, the plates were flat when removed from the vulcanizing apparatus,and in other instances, especially where the printing surface was solid,such plates curved in the wrong direction. The use of the two laminacomprising the shrinkable and non-shrinkable elements 32 and 30 areessential for reliability and a guaranteed proper curvature with everykind of printing surface.

Referring to FIG. 5, there is shown a base member designated generallyby the reference character 50 for making a printing plate 20. Inreferring to member 50 as a base or backing member, it is intended toconnote a carrier for the rubber printing face 2428 of the plate 20. Inother words, the rubber layer 24 with the type 28 integrally formedthereon is laminated to the member 50 in the process of making plate 20,as previously described. Thus, the member 50 is considered a separatearticle of manufacture adapted to be used as a base or carrier for theprinting surfaces of a rubber printing plate and can be supplied as suchto producers of the rubber printing plates.

The member 50 is a composite structure or assemblage of sheet materialsand supplied as such. The sheet member 30A is formed of a non-shrinkablematerial, such as fibrous glass approximately .008 to .010 inch thickand is located to form one outer face of assemblage 50. The

fibrous glass sheet 30A is attached to a sheet of uncured rubber 34A bya layer of rubber cement 52. The cement layer 52 is approximately .010inch thick. The uncured sheet 34A is approximately .020 inch thick andis of approximately 70 durometer hardness. A synthetic rubber such asBuna-N i used. The rubber cement layer 52 can be omitted from theassemblage in the manufacture of many kinds of, printing plates, inwhich case, the combined thickness of sheet 30A and sheet 34A will be.030 inch.

The uncured rubber 34A is adhesively secured by a layer of rubber cement54 to a sheet of shrinkable fabric 32A which, in turn, is secured byrubber cement 56 to the uncured rubber sheet 26A. The sheet 32Acomprises a canvas material such as a Duck canvas No. 11 formed ofcotton and approximately .006 inch thick, although this dimension mayvary. The cement layers 54 and 56 are approximately .002 inch thick. Theuncured rubber layer 26A is approximately .040 inch thick and of 70-90durometer hardness and forms the opposite outer face of the assemblage50.

The assemblage 50 can be supplied as a separate structure or even with asheet of uncured rubber secured on sheet 30A which will form theprinting surface 24-48 of the printing plate 20 when vulcanized. Forinstance, the assemblage 50 can have another layer of rubberapproximately .l87 inch thick which will form the rubber layer 24 andtype 28 of, the plate.

It should be appreciated that the demarcation of layers of sheetmaterial from which the plate 20 is formed, as seen in FIG. 2 is forpurpose of description. Under conditions of vulcanization, the cleardemarcation between rubber layers would not be discernible if plate 20were cut through by a sharp instrument. However, in the assemblage 55),which is prior to curing to form plate 20, such distinct layers ofmaterials is discernible.

The actual manner of mounting the curved printing plate 20 or 40 on aprinting roll or cylinder 22 is of no concern in this invention. Therange of durometer hardnesses set forth for the various rubber layers ofthe printing plate embodying the invention, enables the fabricator toprovide suitably curved printing plates for printing rolls of normal 32,42, or 52 inches presently used in the printing industry. Although it isadvantageous to obtain a complete confirmation of the curvature of theprinting plate to the curvature of the printing roll, it will beappreciated that slight discrepancies therebetween will have little orany adverse consequence since the printing plate already provided withthe built-in curvature need not be bent or stretched to any significantdegree sufiicient to distort the type faces thereof. Consequently, themanufacturer need only make the printing plates in accordance with theinvention with a normal curvature which can be expected to satisfy allof the printing rolls or cylinders in use.

Of considerable advantage herein is the fact that the curved plate 20has a normal condition which does not resist the curvature thereof. Forinstance, in a flat printing plate stretched and bent to conform. to aprinting cylinder. the resilient plate will be based to return to a flatcondition. Thus, after being mounted on the cylinder for some time, theedges curl and the body portions of the plate tend to cup. Also, it canbe appreciated that the mounting of a normally flat printing plate on acylinder is difficult, including providing suitable means for securingthe fiat plate on the cylinder.

It is believed the invention has been described in sufficient detail toenable the skilled artisan to understand and practice the same. Theinvention has been defined in the appended claims in language intendedto be liberally construed commensurate with the contribution made to thearts and sciences by the inventor.

I claim:

1. In a rubber printing plate having a rubber printing surface ofpredetermined durometer hardness for printing directly on corrugatedboard or the like; the herein invention comprising, a carrier structurefor said rubber printing surface comprising, a unitary assemblage havinga bottom rubber layer of substantially greater durometer hardness thansaid printing surface, a top sheet of a relatively non-shrinkablefabric-like material, a shrinkable fabric sheet, and a rubber bondinglayer interposed between said fabric sheets with said shrinkable fabricsheet next adjacent said bottom rubber layer, said carrier having asheet of rubber of said predetermined hardness laminated to said topsheet by conventional vulcanizing procedures to produce said printingsurface with said carrier preset in an arcuate configuration and saidprinting surface substantially free of distortion.

2. A flexible molded printing plate adapted to be mounted on a printingcylinder of a rotary printing machine for direct imprinting oncorrugated paperboard or the like and having a normally arcuate crosssection for enabling the plate to be conformed to said cylindercurvature in mounting with a minimum of distortion of the printingsurface, said plate comprising a laminated molded member having a baserubber layer and a top rubber layer, with the printing intelligencemolded into the top layer, a pair of fabric sheet elements embedded insaid plate bonded together and sandwiched between the top and baserubber layers, one element being formed of a material which is flatprior to molding and which will shrink appreciably during the molding.and the second element being formed of a material which is fiat prior tomolding and which will not shrink appreciably during the molding of theplate, the second element being the upper of the two and closest to thetop rubber layer.

3. A printing plate as described is claim 2 in which the first fabricsheet element is canvas and the second is fibrous glass material.

4. A printing plate as described in claim 2 in which the top rubberlayer is of a durometer substantially less than that of the base layer.

5. A printing plate as described in claim 2 in which the top rubberlayer is formed of a durometer hardness between 20 and 50 and the baselayer is formed of a durometer hardness between 70 and 90.

6. A printing plate as described in claim 2. in which the base layer ismuch thicker than the top layer exclusive of the printing areas.

7. A printing plate as described in claim 2 in which there is a thirdrubber layer between said fabric sheet elements to provide the bondingbetween them.

8. A printing plate as described in claim 7 in which the base and thirdlayers of rubber are of substantially greater durometer hardness thanthat of the top layer.

9. A flexible printing plate adapted to be secured on the cylinder of arotary printing machine for direct printing on corrugated paperboard orthe like comprising, a normally arcuate laminated rubber member having atop printing surface having protruding printing areas and a base, saidprinting surface and base being formed of layers of cured rubber ofdifferent durometer hardness with the base being of greater durometerhardness and substantially thicker than the layer of said printingsurface exclusive of said printing areas, two sheets of fabric and athird rubber layer between said sheets, one sheet being a non-shrinkingfabric material laminated to said printing surface layer and the secondsheet being a shrinkable fabric material laminated to said base layer.

10. A plate as claimed in claim 9 in which said printing surface layeris from 20 to 50 durometer hardness and said base layer is from 70 todurometer hardness.

11. A plate as claimed in claim 10 in which said third layer isapproximately 70 durometer hardness.

12. In a rubber printing plate having a rubber printing surface forprinting on corrugated board or the like; the herein inventioncomprising, a carrier structure for said rubber printing surfacecomprising, a unitary assemblage having a bottom rubber layer ofsubstantially greater durometer hardness than said printing surface, atop sheet of a relatively non-shrinkable fabric-like material, a secondrubber layer and a shrinkable fabric sheet, said second rubber layerbeing interposed between said fabric sheets with said shrinkable fabricsheet next adjacent said bottom rubber layer, said carrier having asheet of rubber laminated to said top sheet by conventional vulcanizingprocedures to produce said printing plate with said carrier preset in anarcuate configuration and said printing surface substantially free ofdistortion, said bottom layer being a greater durometer hardness andthicker than said second rubber layer.

13. The invention as described in claim 12 in which said top sheetcomprises fibrous glass material and said base layer is formed of rubberof 70-90 durometer hardness.

14. The invention as described in claim 13 in which said second rubberlayer is of approximately 70 durometer hardness.

15. A carrier structure for incorporation as an integral part of anormally curved vulcanized rubber printing plate having a type-bearingsurface suitable for printing directly on corrugated paperboard or thelike; said carrier structure comprising, a stacked assemblage including,first and second sheets of uncured rubber and first and second sheets offabric material in alternated arrangement with said first fabric sheetat the top end and said first rubber sheet at the bottom end of theassemblage, said first sheet of rubber being substantially thicker andof greater durometer hardness than the second sheet of rubber, saidfirst fabric sheet being of non-shrinkable material and said secondfabric sheet being of a shrinkable material, said first sheet of fabricadapted to have a rubber printing surface laminated thereover in formingthe printing plate in which said surface is formed of rubber of lesserdurometer hardness than said first rubber sheet.

16. A carrier structure for use in the manufacture of a rubber printingplate having a rubber printing surface of predetermined hardnesssuitable for printing directly on corrugated board or the like and whichcarrier structure is incorporated as an integral part of the finallyvulcanized printing plate: said carrier structure comprising, alaminated assemblage including, a sheet of uncured rubber, a firstfabric sheet of shrinkable material overlying said sheet of uncuredrubber, a second sheet of non-shrinkable fabric overlying the firstfabric sheet and there being a bonding layer of a vulcanizable materialbetween said fabric sheets, said second sheet of fabric adapted to havea rubber printing layer which is of lesser durometer hardness than saidsheet of uncured rubber laminated there over in forming the printingplate.

References Cited in the file of this patent UNITED STATES PATENTS1,369,519 Davis Feb. 22, 1921 1 1,589,024 Wade et al June 15, 19261,941,148 Keltie Dec. 26, 1933 2,028,148 Swan et al Jan. 21, 19362,047,624 Freedlander July 14, 1936 2,271,125 Juve Jan. 27, 19422,284,095 Jordan May 26, 1942 2,489,791 Liles et al Nov. 29, 19492,893,320 Jones July 7,

1. IN A RUBBER PRINTING PLATE HAVING A RUBBER PRINTING SURFACE OFPREDETERMINED DUROMETER HARDNESS FOR PRINTING DIRECTLY ON CORRUGATEDBOARD OR THE LIKE; THE HEREIN INVENTION COMPRISING, A CARRIER STRUCTUREFOR SAID RUBBER PRINTING SURFACE COMPRISING, A UNITARY ASSEMBLAGE HAVINGA BOTTOM RUBBER LAYER OF SUBSTANTIALLY GREATER DUROMETER HARDNESS THANSAID PRINTING SURFACE, A TOP SHEET OF A RELATIVELY NON-SHRINKABLEFABRIC-LIKE MATERIAL, A SHRINKABLE FABRIC SHEET, AND A RUBBER BONDINGLAYER INTERPOSED BETWEEN SAID FABRIC SHEETS WITH SAID SHRINKABLE FABRICSHEET NEXT ADJACENT SAID BOTTOM RUBBER LAYER, SAID CARRIER HAVING ASHEET OF RUBBER OF SAID PREDETERMINED HARDNESS LAMINATED TO AID TOPSHEET BY CONVENTIONAL VULCANIZING PROCEDURES TO PRODUCE SAID PRINTINGSURFACE WITH SAID CARRIER PRESET IN AN ARCUATE CONFIGURATION AND SAIDPRINTING SURFACE SUBSTANTIALLY FREE OF DIRECTION.